package 剑指offer.第1天;

import java.util.Stack;

/**
 * 剑指 Offer 09. 用两个栈实现队列
 用两个栈实现一个队列。队列的声明如下，请实现它的两个函数 appendTail 和 deleteHead ，分别完成在队列尾部插入整数和在队列头部删除整数的功能。(若队列中没有元素，deleteHead 操作返回 -1 )
 示例 1：
 输入：
 ["CQueue","appendTail","deleteHead","deleteHead"]
 [[],[3],[],[]]
 输出：[null,null,3,-1]
 */
class CQueue {
    Stack<Integer> stack1;
    Stack<Integer> stack2;

    public CQueue() {
        stack1 = new Stack<>();
        stack2 = new Stack<>();
    }

    public void appendTail(int value) {
        stack1.add(value);
    }

    public int deleteHead() {
        if (stack2.isEmpty()) {
            if (stack1.isEmpty()) return -1;
            while (!stack1.isEmpty()) {
                stack2.add(stack1.pop());
            }
            return stack2.pop();
        } else return stack2.pop();
    }

    public static void main(String[] args) {
        CQueue obj = new CQueue();
        int param1 = obj.deleteHead();
        System.out.println("param1 = " + param1);
        obj.appendTail(5);
        obj.appendTail(2);
        param1 = obj.deleteHead();
        System.out.println("param1 = " + param1);
        param1 = obj.deleteHead();
        System.out.println("param1 = " + param1);
        param1 = obj.deleteHead();
        System.out.println("param1 = " + param1);
    }
}

/**
 * Your CQueue object will be instantiated and called as such:
 * CQueue obj = new CQueue();
 * obj.appendTail(value);
 * int param_2 = obj.deleteHead();
 */